Coaxial electrical cables are well known, such cables generally being terminated by the use of electrical connectors having coaxial conductive members separated by dielectric material.
Also known are shielded electrical cables comprising one or more insulated signal conductors surrounded by a shielding layer formed, for example, by a metal foil. To facilitate termination of such a cable, a further uninsulated conductor is sometimes provided between the shielding layer and the insulation of the signal conductor or conductors, termination of this further conductor constituting termination of the shielding layer. Such a cable is disclosed in U.S. Pat. No. 3,775,552.
Both these known forms of cable normally require the use of specifically designed connectors for termination, these connectors not being suitable for the use of mass termination techniques, that is the simultaneous connection of a plurality of conductors to individual contacts in a connector, but requiring individual attention. This is a particular problem with cables comprising a plurality of conductors arranged in a planar array in a common insulating body, when it is desired to use a connector having so-called slotted plate contacts each having a plate portion having a slot open to one edge of the plate into which slot a conductor can be urged such that the slot walls grip the conductor and establish an electrical connection between the conductor and the contact.
In U.S. patent application Ser. No. 383,638 filed June, 1, 1982, an electrical cable is disclosed comprising an outer layer of insulating material surrounding a signal conductor and an associated ground conductor and a common shielding layer in electrical contact with the ground conductor but separated from the signal conductor by an inner layer of insulating material surrounding the signal conductor, characterized in that the signal and ground conductors extend in spaced parallel relationship in a common plane, each surrounded by an individual outer layer of insulating material, the two outer layers of insulating material being integrally formed with a web extending between the two outer layers of insulating material, the shielding layer extending about the inner layer of insulating material on the signal conductor, through the web, and about the ground conductor.
Such a cable has the advantage that the spacing between the signal and ground conductors can be set to accord with the spacing between the relevant contacts in a connector to be used to terminate the cable whereby a mass termination technique can be used without the operator having to rearrange the cable conductors.
Preferably the signal and ground conductors are substantially the same size, and the diameter of the outer layer of insulating material surrounding the ground conductor is substantially equal to the diameter of the inner layer of insulating material surrounding the signal conductor.
Such a choice of dimensions enables the use of slotted plate contacts having the same size slots for termination of the signal and ground conductors, thus facilitating assembly of a connector to be used to terminate the cable since identical contacts can be used for all conductors. For termination, the outer layer of insulating material and the shielding layer are stripped from a length of the signal conductor, thus leaving an insulated signal conductor and a ground conductor surrounded by the shielding layer and the outer layer of insulating material, of substantially equal diameter.
A composite cable can be formed from a plurality of such cables arranged in side-by-side relationship, the cables being connected by an integrally formed web extending between the outer layers of insulating material of the cables.
Such a composite cable can be readily mass terminated with a minimum of pre-preparation using conventional techniques and a connector having a plurality of contacts with identical slotted plate contact portions, the conductors in the cable being spaced in accordance with the spacing of the associated contacts of the connector.
In the cable specifically disclosed in the above-noted application, each signal conductor has an individually associated ground conductor, each pair of conductors having an individually associated shielding layer.
However, such an arrangement is not always essential, it being possible for a single ground conductor to be associated with a plurality of signal conductors.
In GB-A-2047947, such a cable is disclosed in which the shielding layer surrounding the inner layer of insulating material surrounding each signal conductor, extending through the webs, and about the ground conductor is formed from a single layer of conductive polymer. However, this prior specification does not disclose the conductor and insulation size relationships discussed above.